<html>

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>布尔值关灯</title>
</head>

<body>
    <img id="d" src="./img/pic_bulboff.gif">
</body>
<script>
    var deng = true;
    if (deng == false) { 
        let img = document.getElementById("d");
        img.src = "./pic_bulbon.gif";
    }
</script>

</html>